This invention relates in general to communication systems, and more specifically to a method and apparatus for limiting message loss and message latency in a messaging system.
Information Services (IS) messages are becoming increasingly popular in today""s wireless messaging systems. The IS messages can provide periodic reporting of stock quotes, sports scores, news, weather, and other information that may be of general interest. Such messages preferably are sent as group-call messages to conserve air time. A group-call message is addressed to a single address and will be received and decoded by a plurality of subscriber units that have subscribed to the particular type of information service associated with the address, e.g., news. Individual subscriber units can subscribe to multiple types of information services, up to the capacity of the subscriber unit to store IS addresses.
For added capacity, many messaging systems operate on a plurality of logical channels which operate concurrently. Each subscriber unit is assigned to one of the logical channels as its control channel. The subscriber unit monitors the control channel for IS and personal addresses active in the subscriber unit. When the subscriber unit decodes one of its personal or IS addresses, it then continues to monitor the control channel for a vector which will tell the subscriber unit what channel and what time slot it should go to in order to receive its message (or fragment thereof).
In prior art systems, the devices which schedule transmissions of addresses and message fragments on multiple logical channels have ignored possible conflicts among all the addresses programmed into each subscriber unit. As a result, some messages have been delivered with higher latency than desired, while other messages have been missed altogether, as will be explained further below.
Thus, what is needed is a method and apparatus that can limit missed messages and high latency that can result when a mix of personal messages and group-call messages exist in a multi-channel messaging system.
An aspect of the present invention is a method for limiting message loss and message latency in a messaging system which transmits to a subscriber unit on a plurality of logical channels operating concurrently. The method comprises the steps of transmitting control information for the subscriber unit on a control channel assigned to the subscriber unit, and transmitting a personal message fragment intended for the subscriber unit on a first logical channel. The method further comprises the steps of transmitting a group-call message fragment that may be intended for the subscriber unit on a second logical channel, and before the transmitting steps, scheduling the transmitting steps such that a probability that the personal and group-call message fragments will overlap temporally with one another and that either of the fragments will overlap temporally with the control information is reduced.
Another aspect of the present invention is a controller for limiting message loss and message latency in a messaging system which transmits to a subscriber unit on a plurality of logical channels operating concurrently. The controller comprises a network interface for receiving messages to be transmitted, and a processing system coupled to the network interface for processing the messages. The controller further comprises a base station interface coupled to the processing system for controlling a transmitter to transmit the messages. The processing system is programmed to cooperate with the transmitter to transmit control information for the subscriber unit on a control channel assigned to the subscriber unit, and to cooperate with the transmitter to transmit a personal message fragment intended for the subscriber unit on a first logical channel. The processing system is further programmed to cooperate with the transmitter to transmit a group-call message fragment that may be intended for the subscriber unit on a second logical channel; and before enabling a transmission of the control information and the fragments, to schedule the transmission such that a probability that the personal and group-call message fragments will overlap temporally with one another and that either of the fragments will overlap temporally with the control information is reduced.